1. Technical Field
The present invention relates to printing apparatuses suitable for use as, for example, printers, and particularly to improvements in determination of whether or not a cleaning operation for recording heads is started at a low ink level.
2. Related Art
A type of printer is known that performs printing by ejecting ink supplied from an ink cartridge (ink tank) from a recording head onto a recording medium. This type of printer can fail to print successfully because of phenomena such as nozzle clogging due to increased ink viscosity resulting from evaporation of ink solvent from nozzle orifices of the recording head, deposition of dust on the nozzle orifices, and intrusion of bubbles into the nozzles upon replacement of the cartridge.
To recover the printer from such phenomena, as is known in the related art, a cleaning operation is performed by sucking ink from the nozzles of the recording head to eliminate the problems such as clogging, deposition of dust, and intrusion of bubbles at the nozzles of the recording head.
Specifically, as discussed in JP-A-2000-153622 (Patent Document 1), JP-A-2005-104089 (Patent Document 2), and JP-A-11-5300 (Patent Document 3), the cleaning operation is performed by a cleaning mechanism provided in a printer. The cleaning mechanism includes a cap, an ink drain channel communicating with the cap, and a pump provided somewhere in the ink drain channel. The nozzles of the recording head are covered with the cap before the pump is driven to reduce the inner pressure of the cap via the ink drain channel. This causes ink to be sucked from the nozzles of the recording head and drained into a waste ink tank, thus eliminating the problems such as nozzle clogging.
During the cleaning operation, the ink supply from the ink cartridge must not be interrupted because, for example, the ink drained into the cap, which has therefore been contaminated, would flow back, thus complicating maintenance.
Accordingly, whether or not the cleaning operation is permitted is determined with respect to the ink level. According to JP-A-2000-296627 (Patent Document 4), an ink-end level is set on the basis of the amount of ink stored in the ink tank, and notification requesting replacement of the ink tank is provided when a total ink consumption calculated by a soft counter or dot counter exceeds the ink-end level (see paragraphs 0044 and 0053-0055 of Patent Document 4). The total ink consumption is the sum of the cumulative ink consumption count and the consumption count for the next cleaning operation. The ink-end level is a predetermined level depending on the type of ink cartridge.
The above method, however, results in a significant cumulative error because the soft counter or dot counter counts the total ink consumption in such a manner that safety ejection is ensured to prevent ejection failure. This means that the determination that the cleaning operation is prohibited is made even if the ink actually remains in the ink tank. Hence, the replacement of the ink tank is requested even if the ink level is actually sufficient for cleaning. This applies not only to cleaning but also to printing.
Another approach uses an ink-level sensor built into an ink tank (ink cartridge) to detect ink depletion and provide notification requesting replacement of the ink tank. In the related art, however, the notification requesting replacement of the ink tank is provided before the sensor detects ink depletion because the total ink consumption exceeds the ink-end level.
In the second embodiment discussed in Patent Document 4, the ink tank is provided with a detection switch that is actuated by a mechanical ink-end sensor. A near-end point is detected when the detection switch is actuated, and afterwards a soft counter or dot counter is used to permit printing or cleaning on the basis of the amount of ink to be used in printing or cleaning (see paragraphs 0060-0066 and FIGS. 5 and 6 of Patent Document 4).